1. Field of the Invention
The present invention relates to a zoom lens system, an imaging device and a camera. In particular, the present invention relates to: a zoom lens system that has a reduced overall length, a high resolution, and a variable magnification ratio as high as 9 or greater and that is satisfactorily adaptable for wide-angle image taking where the view angle at a wide-angle limit is 70° or greater; an imaging device employing this zoom lens system; and a thin and compact camera employing this imaging device.
2. Description of the Background Art
With recent progress in the development of solid-state image sensors such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal-Oxide Semiconductor) having a high pixel, digital still cameras and digital video cameras are rapidly spreading that employ an imaging device including an imaging optical system of high optical performance corresponding to the above-mentioned solid-state image sensors of a high pixel.
Among these, various zoom lens systems have been proposed that can realize a compact type camera provided with, in addition to a high resolution, a zoom function of high magnification such as a variable magnification ratio as high as approximately 9 or greater.
For example, Japanese Laid-Open Patent Publication No. 2006-113453 discloses a zoom lens that, in order from the object side to the image side, comprises three lens units of positive, negative and positive, and further a subsequent lens unit, wherein intervals between the individual lens units vary such that the interval between the first lens unit and the second lens unit increases and the interval between the second lens unit and the third lens unit decreases at a telephoto limit in comparison with a wide-angle limit, and wherein a negative lens where the Abbe number and the partial dispersion ratio satisfy a particular relation is included in the third lens unit. In this zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2006-113453, chromatic aberration is compensated satisfactory in a wide zoom range, so that high optical performance is obtained.
Further, Japanese Laid-Open Patent Publication No. 2005-017915 discloses a zoom lens that, in order from the object side to the image side, comprises five lens units of positive, negative, positive, positive and positive, wherein intervals between the individual lens units vary such that at least the interval between the first lens unit and the second lens unit increases while the interval between the third lens unit and the second lens unit decreases and the interval between the fourth lens unit and the third lens unit decreases during magnification change from a wide-angle limit to a telephoto limit, and wherein the interval at a wide-angle limit and the interval at a telephoto limit between the third lens unit and the fourth lens satisfy a particular relation. This zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2005-017915 has a high variable magnification ratio, a high brightness, a small number of lenses, a low price, and compactness.
Moreover, Japanese Laid-Open Patent Publication No. 2001-194590 discloses an imaging lens device provided with: a zoom lens that, in order from the object side to the image side, comprises two lens units of positive and negative and further a subsequent lens unit, wherein during magnification change from a wide-angle limit to a telephoto limit, the second lens unit moves such as to be always located on the image side relative to a position at a wide-angle limit, wherein the first lens unit consists of three or fewer lenses, in total, including at least one negative lens and at least one positive lens, and wherein at least one positive lens in the first lens unit has particular refractive index and Abbe number; and an image sensor. This zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2001-194590 has high performance, and has a reduced size and a high variable magnification simultaneously.
Nevertheless, although the zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2006-113453 has high optical performance and simultaneously a high magnification zoom function such as a variable magnification ratio of approximately 9 to 10 or the like, this zoom lens does not have a configuration applicable to wide-angle image taking where the view angle at a wide-angle limit is, for example, 70° or greater.
Further, the two zoom lenses disclosed in Japanese Laid-Open Patent Publication No. 2005-017915 and Japanese Laid-Open Patent Publication No. 2001-194590 also have a high magnification zoom function and simultaneously a reduced size, but do not have a configuration satisfactorily suitable for wide-angle image taking where the view angle at a wide-angle limit is, for example, 70° or greater.